The problem is you're trying to transform a DOCX document with the TEI P5 DOCX scenario, which is meant to transform from TEI P5 to DOCX and not the other way around as you seem to expect it to. There is also a DOCX TEI P5 scenario which, I'm guessing, is the one you were looking for.

I see that in your configuration the DOCX document.xml is now seen by Oxygen as the TEI P5 document type, so that's why you're seeing the TEI P5 specific scenarios for this DOCX document. I'm guessing you've made changes to the association rules from the TEI P5 framework and now, probably, many more XML documents are considered TEI P5 (even though they are not). Please make sure the association rules are strict enough to avoid this.

Actually, I don't see the "DOCX TEI P5" option in Oxygen 15 based on the most recent download of the TEI transformation files, either within the frameworks folder or when I designate a custom frameworks folder. (I do see them in 14.2, though.) The file does have the build-to.xml and build-from.xml

I apologize. I was mistaken
The option of DOCX TEI P5 does appear among the options when selecting from the frameworks files in the oxygen frameworks folder. It does not appear when redirecting to a custom frameworks folder.

The scenario DOCX TEI P5 is included in the OOXML framework, because it's applied to a DOCX (OOXML) document. So, if you've selected a custom frameworks folder and only have there a TEI P5 framework, that explains the lack of a DOCX scenario. If you want to have your custom frameworks folder self contained, you should also copy the OOXML framework folder.

Is there a variable that will point to this custom_frameworks directory? I want to distribute my framework to our authors who are on a mix of Windows and Mac, so I need to build a relative path to the catalog, css, schematron, etc. based on this custom_frameworks directory location.

Is there a variable that will point to this custom_frameworks directory? I want to distribute my framework to our authors who are on a mix of Windows and Mac, so I need to build a relative path to the catalog, css, schematron, etc. based on this custom_frameworks directory location.

I should point out, the additional framework directory is external to the oXygen installation in an SVN folder that our organization uses. I need a variable that resolves to this external location.